Modulation system



June 2, 1942. J. sTElNMx-:Tz 2,284,689

MODULATION SYSTEM Filed July 22, 1939 Patented 'June 2, 1.942

MODULATION SYSTEM Joachim Steinmetz', Berlin-Tempelhof, Germany,

assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, acompany Application July zz, 1939, serial No. 285,839 In Germany July26, 1938 1 Claim.

Ultra-short wave transmitters comprising a control stage and a modulatorstage have the disadvantage that the anodal retroaction affects thefrequency of the control transmitter, thus causing this frequency tofluctuate. Therefore, electronic screen grid tubes have been employed inthe main transmitter in order toreduce the anodal retroaction, and thescreen grid has been earthed. In the case of ultra-short waves, how

ever, the line that extends from the screen grid to earth constitutes aconsiderable inductance. As a result there is a retroaction lfrom thescreen grid on the control grid. Such retroaction has the same drawbacksas an anodal retroaction because in this case -too the control frequencyundergoes a detrimental variation.

The high frequency relationships are represented in the drawing, inwhich Fig. 1 is a diagrammatic representation of the essential featuresof modulator stages as provided by the invention, Fig. 2 is a diagramthat serves to explain the idea of the invention.

The control frequency, that is, the frequency arriving from the controltransmitter T, is conveyed to the control grid G of a pentode of whichthe suppressor is not shown since it is immaterial to the invention, asindicated in Fig. 1. The modulation current from source M is applied tothe screen grid SG. Included in the anode circuit is a' Lecher line Lwhich serves for tuning. The interelectrode capacities are representedas condensers shown in dotted lines. From Fig. 2 it will be seen thatthe intereiectrode capacities may be thought to be comprised in a bridgeconnection. The lpoints I, 2 have a mutual phase difference of 180degrees with respect to ground and may be considered as the feedingpoints.

In accordance with the invention a capacity Cx is connected in parallelwith the grid-anode capacity CAG and this capacity Cx is made so greatthat the total current flowing through Cac and Cx equals the current'through Cscc., the bridge thus being balanced. The control grid G onthe one hand and ground on the other hand constitute the two diagonallyopposite corners of the bridge between which corners there is zeropotential difference under balance conditions. The novel arrangementacts perfectly to compensate the screen grid retroaction so that thecontrol grid will ynot be affected to any extent.

What is claimed is:

An ultra-short wave modulating arrangement comprising a tube having acathode, an anode, a screen grid, and a control grid, a plate impedanceconnected between said anode and ground, screen grid groundingconnections having inherent impedance joining said screen grid toground, a carrier frequency source connected to apply a carrierfrequency potential between ground and said control grid, a source ofsignaling potential Vconnected between the screen grid and ground Theinvention now consists in so balancing the A whereby an oppositelyphased signaling-bequem cy potential is established between said anodeand ground, and a condenser connected between said anode and saidcontrol grid wherebysaid condenser and the inherent capacity betweensaid anode and control grid in parallel constitute a first arm of abridge, of which a second arm is constituted by the inherent capacitybetween said. screen grid and said control grid and of which theremaining two arms are constituted by said plate impedance to ground andsaid inherent impedance of the screen grid grounding connectionsrespectively, said first and second arms being'connected in seriesbetween said anode and said screen grid, and said condenser hav.

ing a value such that the resultant voltage developed between said anodeand said screen grid due to said two signal frequency potentials causesequal cin'rents to flow through said first and second arms. JOACHIMSTEINm.

